Keying system



0d. 16, 1934. HRODER 1,977,594

KEYING SYSTEM Original Filed Sept. 9, 1930 INVENTOR HANS RODER BY V ATTORNEY Patented Oct. 16, 1934 UNITED STATES KEYIN G SYSTEM Hans Roder, Scotia, N. Y., assignor to Telefunken Gesellschaft fur Drahtlose Telegraphic m. b. 11., Berlin, Germany, a corporation of Germany Application September 9, 1930, Serial No.,480,'715

Renewed February 3, 1934. In Germany September 17, 1929 7 Claims. (Cl. 25 -17) 7 The present invention relates to a method and means for eliminating key shocks which are produced by the key operation of the transmitter tube. In accordance with the present invention,

the keying action is adapted to take place in the tube input circuit.

It has been known that whenever a receiver is installed in the neighborhood of a transmitter, reception is usually more or less seriously dis- 0 turbed by the latter. Indeed, each key operation of the transmitter and each rise and fall of the impulse becomes audible in the receiver in the form of a crackling noise known as a key shock.

If the transmitter and the receiver are mounted within one and the same room, and if, in addition, the sending and the receiving antenna are disposed close together or, whatis worse, underneath each other, reception becomes practically impossible so long as the transmitter is in operation. It is hopeless to attempt to eliminate these key shocks by radio frequency stoppers inasmuch as the rapid initiation of" the oscillations embodies a practically continuous frequency spectrum. Hence, ways and means must be adopted for the transmitter whereby such frequency spectrum will be limited. This may be insured by so regulating the rise and fall of the key signals that the sharp edges of the signals will be rounded, as it were.

By copending application filed September 9,

1930, Serial No. 480,714, a still further system is disclosed by which it ispossible to avoid'th'e key shocks in arrangements wherein the keying action takes place in theplate circuit of the transr mitter tubes. The present invention, however,

discloses a method to this end applicable to transmitter tubes whose grid direct current is modulated.

The invention has been illustrated in its preferred embodiments by the accompanying drawing wherein:

Fig. 1 illustrates one form of transmitter circult; and,

Fig.2 illustrates an improved form of the arrangement of Fig; 1 wherein the invention has been applied to the use of a filter circuit, for example. I

Modulating a separately excited tube amplifier of the general type shown and illustrated in Fig. 1 of the drawings wherein a series of interruptions or chopping actions of the grid direct current are produced by means of op ning and closing a key T, the following observations can be made: (1). Upon depressing. the key Tthe rise of the antenna current occurs in accordance with the time constant RXC, if the capacity C had previously been charged negatively to a point so current happens in accordance with the time constant CXRX, where Rx the variable internal resistance grid-filament of the rectifier. This time interval or period is far greater than in case (1) (3) When interrupting the grid direct current, condenser C is able to become charged up only to the crest value of the grid alternating current As a result, owing to the inverseamplification'factor (plate reaction) of the tube, a small amount of current will pass to the plate upon each positive grid potential crest, and the result is that the antenna current will not be re-' duced fully to Zero. In fact, complete blocking of the antenna current will happen only when capacity C is charged up to 1.5 to 2 times the crest value of the grid alternating current potential.

To refer now to Fig. 2 showing a preferred embodiment of the invention wherein the inconveniehce of the arrangement shown by Fig. 1 is obviated, it will be seen that the grid direct current is here passed through a filter chain comprising resistances R and condensers C. In parallel relation to the first unit of this filter may be arranged a rectifier tube G fed with audio frequency energy and furnished with resistances Rl-and R2. When the key T is depressed or closed, the grid of the rectifier G will be charged negatively. Under such conditions tube G is blocked at once, and the condensers C are discharged in accordance with the time-constant of filter RC, and in accordance therewith the negative potential at the grid of the carrier waveamplifier tube decreases and the antenna current increases. Upon releasing or opening the key T the resistance R2 is short-circuited by way of the back contact of the saidkey, and the grid of tube G is connected with the cathode. Hence, the rectifier G becomes conductive and the charging up of the condensers C begins. The rectifier alternating current potential E5 is 1.5 to 2 times higher than The charging of the condensers C for this reason occurs substantially faster than when the rectifier action of the gridfilament circuit of the modulated stage is called upon to charge up the filter alone.

-Other modifications and changes may suggest themselves to those skilled in the art to which the invention relates, and I, therefore, believe myself to be entitled to make and use any and all of such modifications as fall fairly within the spirit and scope of the hereinafter appended claims.

Having now described my invention, what I claim and desire to secure by Letters Patent is the following: 1. In a keying system, a thermionic amplifying device having an input circuit, a source of high frequency oscillating voltage connectedwith thel input circuit, a capacity element connected in tube control electrode and to one terminal of said.

the direct current path between the control electrode and filament of the thermionic device for interrupting the direct current path, a resistance having one terminal connected with the capacity, said resistance being of such value that the product of the resistance value and the capacity value is equal to a time constant at least several times the period of the supplied oscillatory voltage, a contact means connecting the other terminal of said resistance to the other terminal of said capacity for completing upon closure of said contact the direct current path of the thermionic device input circuit, and auxiliary amplifying device, a capacity element connected amplify the impressed high frequency voltages,

to form a part of the input circuit of the amplifying device, an operating key connected to one terminal of. the capacity element, a resistance element and a source of current connected in parallel with each-other connected to the second terminal of the capacity element andalternately adapted to have the opposite ends thereof contact with the operating key in its open and closed positions whereby in one position of the key energy from the current source is stored in the capacity element and the amplifying device is; rendered inoperative to amplify the supplied voltages and in the other position of the key the amplifying device is biased toa state operative to transmit amplified impressed voltage signals, and an output circuit connected with the amplifying device to utilize the output currents therefrom. e

,3. In combination, a thermionic amplifying tube having input and output circuits, means to supply high frequency oscillating voltages to the input circuit of the amplifying device, a laddertype filter comprising shunt capacity and series resistance having the terminals at one end connected with the grid and filament electrodes of the amplifying tube, an operating key connected between the terminals at the other end of the filter, a source of current for charging the filtercapacity element in one position of the operating key to render the amplifying tube inoperative to and means connected with the operating key for permitting upon positioning the key in a second position only slow dissipation of the charge from the capacity element. e. In combination, a thermionic relay tube having a grid and a cathode, a circuit for applying currentoscillations between the grid and cathode of said tube, said circuit including a condenser which becomes charged when current due to grid :1 rectification of the current oscillations applied tosaid circuit fiows therein, thecharge on said condenser applying a potential to the grid of said tube which biases the same substantially to cut- 0ff, a.. second circuit including a key which, in

(Q the closed position, shunts said condenser to discharge the same and remove the bias from said grid to permit the flow of current in said tube,

and a'third circuit including a sourceof poten-,-

tial and a contact'on which said key bearsin '55 jits'open positionto connect said source of potential with said condenser to charge the same at a rate higher than the rate at which said condenser is charged by current due to grid rectification in said first named circuit.

5. In combination, a thermionic relay tube having a grid and a cathode, a circuit for applying current oscillations between the grid and cathode of said tube, said circuit including a condenser which becomes charged when current due to grid rectification of the oscillations applied to said circuit flows therein, the charge on said condenser applying a potential to the grid of said tube which biaseslthe same substantially to cut-off, a second circuit including an impedance and a key which, in the closed position, shunts said condenser to discharge the same and remove the bias from said grid to permit the how of current in said tube, and (a third circuit including a source of, potential in the form of a thermionic rectifier, and a contact on which said key bears in its open position to connect said source of potential in parallel with said condenser to charge the same at a rate higher than the rate at which said condenser is charged by current due to gridrectification in said first named circuit.

6. In a keying system, a thermionic tubehaving an input circuit on which oscillatory energy may be impressed, a condenser connected with a direct current path between the control electrode and filament of said tube,, said condenser being charged by the current in said path due to grid rectification, a resistance having one terminal connected with the control electrode of the tube, said resistance being of such a value that the produce of the resistive value and the capacitive value of the condenser is equal to a time constant at least several times the period of the supplied'oscillatory energy, a contact device in the grid current, path for completing upon closure of' the contact device the direct current path between the control grid and filament of the tube,

and an auxiliary contact'and circuit operative,

upon opening the aforesaid contact device for charging the capacity of the condenser to a voltage greater than the peak voltage of the oscillating energy supplied to the input circuit of the tube and at a rate more rapid than the charge produced upon the capacity of the condenser due solely to the current of the thermionic tube due to grid rectification.

7. In combination, a thermionic relay tube having a grid and a filament, a circuit for applying current oscillations between the grid and filament of said tube, said circuit including a system of resistances and condensers which become charged when current due to grid rectification of the oscillations applied tosa-id circuit flows therein,

the charge on said system applying a potential to the grid of said tube which biases the same substantially tocut-ofi, a second circuit includat which said-condenser 'system is charged by, current due togrid rectification in said firstf 1 HANS RODER.

named circuit. a 

